1. Field of the Invention
This invention relates to feedback control technology, and more particularly, to an airflow feedback control method and apparatus for fan filter unit (FFU), which is designed for use with a fan filter unit that is widely used in semiconductor fabrication factories, for controlling the fan filter unit to generate an amount of airflow equal to a preset desired amount.
2. Description of Related Art
Fan filter unit (FFU) is a widely used dust-clearing device in the semiconductor industry for installation in cleanrooms, typically on the ceiling, for the purpose of generating a downstream of airflow from the top for the purpose of blowing away dust particles or any other tiny dirt objects in the cleanroom so as to provide a substantially dust-free environment for the fabrication of semiconductor chips.
FIG. 1 is a schematic diagram showing a sectional view of a conventional fan filter unit 10, which includes a fan rotor 11 and a bell inlet 12, wherein the bell inlet 12 has an inwardly-tapered air passage with a circularly-curved inner wall 13. When the fan rotor 11 rotates, it can suck air from the atmosphere into the inlet 21 and generate a downward-going airflow which flows via the outlet 22 to the bottom of the fan filter unit 10, thereby outputting a downstream of airflow for dust-clearing purpose.
Fundamentally, it is desired that fan filter units be capable of continuously generating a fixed and unchanging amount of airflow to the cleanroom; to ensure the cleaning capability of the airflow system. In addition, when a plurality of fan filter units are installed in array in a cleanroom, it is highly desired that all of the fan filter units in the array all generate an equal amount of airflow; otherwise, it would undesirably cause sideward-going airflows that would degrade the dust-clearing effect.
One solution to the aforementioned problem is to make all fan filter units run at the same speed. However, in practice, it would be highly difficult to set all fan filter units to run at exactly the same speed. A minor difference in speed would nevertheless cause the problem of sideward-going airflows.
Another solution to the aforementioned problem is to use a speed feedback control method to control each fan filter unit to run at a preset desired speed. In practice, however, even though it is feasible to control each fan filter unit to run at a preset desired speed, the airflow amount would nevertheless be affected by a change in the air pressure or a nonuniform distribution of the air pressure in the cleanroom, which can be caused by, for example, a change in the amount of equipment or personnel in the cleanroom, inappropriate cleanroom design, refashion to the cleanroom, replacement of the filter in the fan filter unit, and so on. Under these conditions, the amount of airflow from a fixed-speed fan filter unit would nevertheless be deviated from the desired amount.
It is therefore an objective of this invention to provide an airflow feedback control method and apparatus for controlling a fan filter unit to continuously generate an amount of airflow equal to a preset desired amount irrespective of any changes in the air pressure in the cleanroom.
The airflow feedback control method and apparatus for fan filter unit according to the invention is characterized by that it utilizes airflow as feedback parameter, rather than utilizing motor speed as feedback parameter by prior art. This feature allows the fan filter unit to continuously generate a fixed amount of airflow equal to a preset desired amount even if there is a pressure change at the site of installation. The FFU airflow feedback control method and apparatus of the invention is therefore more advantageous to use than prior art.